DE102022101787A1 - LASER DIODE DEVICE AND METHOD OF MAKING AT LEAST ONE PHOTONIC CRYSTAL STRUCTURE FOR A LASER DIODE DEVICE - Google Patents

Abstract

A laser diode component (1) is specified comprising
- a semiconductor layer stack (2) which has an active zone (4) for emitting laser radiation,
- comprising a photonic crystal structure (7).
- a crystalline material (8),
- a plurality of structured areas (9, 9A, 9B, 9C), each of which is laterally delimited by at least one delimiting surface (7A), and
- at least one side surface (7B, 7C) which laterally delimits the photonic crystal structure (7), at least one of the delimiting surfaces (7A) of the structured regions (9, 9A, 9B, 9C) and/or at least one of the side surfaces (7B, 7C) of the photonic crystal structure (7) extending along crystal planes of the crystalline material (8).
A method for producing at least one photonic crystal structure (7) for a laser diode component (1) is also specified.

Description

A laser diode component and a method for producing at least one photonic crystal structure for a laser diode component are specified. For example, the laser diode component is a so-called PCSEL (Photonic Crystal Surface Emitting Laser).

For example, it is characteristic of a PCSEL that laser modes form in a plane of the photonic crystal due to the photonic band structure and laser radiation can be coupled out in a vertical direction, ie perpendicular to the plane of the photonic crystal.

For photonic crystals of high quality, structural elements of the photonic crystal should be arranged as uniformly as possible and have smooth edges. For example, when using photo technology and dry-chemical etching to produce the structural elements, damage to the material occurs in addition to irregular shapes.

Furthermore, in order to be able to produce small pixels in a display, additionally required mirror elements should take up as little space as possible.

One problem to be solved in the present case is, inter alia, to specify a powerful laser diode component. A further problem to be solved in the present case consists, inter alia, of specifying a method for producing at least one photonic crystal structure of higher quality for a laser diode component.

These objects are achieved, inter alia, by a laser diode component and a method for producing at least one photonic crystal structure for a laser diode component having the features of the independent claims.

Further advantages and configurations of a laser diode component and a method for producing at least one photonic crystal structure for a laser diode component are the subject matter of the dependent claims.

In accordance with at least one embodiment of a laser diode component, the latter comprises a semiconductor layer stack which has an active zone for emitting laser radiation. The laser diode component is suitable, for example, for emitting laser radiation from the spectral range from ultraviolet to infrared.

The active zone can have a sequence of individual layers, by means of which a quantum well structure, in particular a single quantum well structure (SQW, single quantum well) or multiple quantum well structure (MQW, multiple quantum well), is formed.

In accordance with at least one embodiment or configuration, the semiconductor layer stack has a first semiconductor region of a first conductivity type, for example an n-doped semiconductor region, and a second semiconductor region of a second conductivity type, for example a p-doped semiconductor region. The active zone can be arranged between the first and second semiconductor region. The first and second semiconductor regions can each have a sequence of individual layers, some of which can be undoped or lightly doped. The individual layers can be layers deposited epitaxially on a growth substrate.

For example, materials based on arsenide, phosphide or nitride compound semiconductors can be considered for the semiconductor regions or individual layers of the semiconductor layer stack. "Based on arsenide, phosphide or nitride compound semiconductors" in the present context means that the semiconductor layers contain Al _n Ga _m In _1-nm As, Al _n Ga _m In _1-nm P, In _{n Ga 1-n} As _m P _1-m or Al _n Ga _m In _1-nm N, where 0 ≤ n ≤ 1, 0 < m < 1 and n+m ≤ 1. This material does not necessarily have to have a mathematically exact composition according to the above formula. Rather, it may have one or more dopants as well as additional components that do not substantially change the characteristic physical properties of the Al _n Ga _m In _1-nm As, Al _n Ga _m In _1-nm P, In _n Ga _1-n As _m P _1-m or Al _n Ga _m In _1-nm N material. For the sake of simplicity, however, the above formula only contains the essential components of the crystal lattice (Al, Ga, In, As or P or N), even if these can be partially replaced by small amounts of other substances. A quinternary semiconductor made of Al, Ga, In (group III) and P and As (group V) is also conceivable.

In accordance with at least one embodiment, the laser diode component has a photonic crystal structure.

A “photonic crystal structure” means a structure with a periodically changing refractive index in which a photonic band structure is formed that has forbidden energy regions in which electromagnetic waves cannot propagate.

The photonic crystal structure may include a crystalline material. A “crystalline material” is to be understood, for example, as a material whose building blocks are predominantly arranged in a crystal structure.

Furthermore, the photonic crystal structure can have a plurality of structured regions, each of which is laterally delimited by at least one delimiting surface. At least one of the boundary surfaces of the structured regions can each extend along a crystal plane of the crystalline material. The structured areas can each be bounded on all sides by boundary surfaces that run along crystal planes of the crystalline material. In particular, the boundary surface extending along a crystal plane is a crystal facet of the crystalline material. Alignment of the structured areas on crystal planes or crystal facets leads to particularly smooth and uniform structures and thus to a photonic crystal structure of high quality. As a result, the efficiency and service life of the laser diode component can be increased.

In particular, the structured areas are regularly arranged in the photonic crystal structure and bring about a periodic change in the refractive index. The structured areas can have dimensions and distances in the range of a wavelength of the laser radiation and are therefore in the range of fractions of a micrometer.

Furthermore, the photonic crystal structure can have at least one side surface, which delimits it laterally. In this case, at least one of the side surfaces of the photonic crystal structure can extend along a crystal plane of the crystalline material. In particular, the side face extending along a crystal plane is a crystal facet of the crystalline material.

The one or more side surfaces form a border of the photonic crystal structure. In particular, the structured areas are arranged at a distance from the border, which leads to an in-phase reflection.

• - einen Halbleiterschichtenstapel, der eine aktive Zone zur Emission von Laserstrahlung aufweist,
• - eine photonische Kristallstruktur umfassend
  • - ein kristallines Material,
  • - eine Mehrzahl von strukturierten Bereichen, welche jeweils durch zumindest eine Begrenzungsfläche seitlich begrenzt sind, und
  • - zumindest eine Seitenfläche, welche die photonische Kristallstruktur seitlich begrenzt, wobei

sich jeweils zumindest eine der Begrenzungsflächen der strukturierten Bereiche und/oder zumindest eine der Seitenflächen der photonischen Kristallstruktur entlang von Kristallebenen des kristallinen Materials erstrecken.According to at least one embodiment of a laser diode component, this comprises:

• - a semiconductor layer stack which has an active zone for emitting laser radiation,
• - comprising a photonic crystal structure
  • - a crystalline material,
  • - a plurality of structured areas, each of which is laterally delimited by at least one delimiting surface, and
  • - At least one side surface which delimits the photonic crystal structure laterally, wherein

in each case at least one of the boundary surfaces of the structured regions and/or at least one of the side surfaces of the photonic crystal structure extend along crystal planes of the crystalline material.

In the laser diode component, the photonic crystal structure fulfills in particular the function of a lateral resonator. In this case, an electrical field of the radiation is constricted in the horizontal or lateral direction by the photonic crystal structure. For example, in the present case, laser radiation is to be understood as meaning coherent radiation in the fundamental mode of the resonator. In particular, the crystalline material is transparent to the radiation emitted by the active zone.

In accordance with at least one embodiment or configuration, the photonic crystal structure is arranged in the semiconductor layer stack. The photonic crystal structure is advantageously arranged as close as possible to the active zone. The semiconductor layer stack can have a first cladding layer arranged in the first semiconductor region and a second cladding layer arranged in the second semiconductor region, between which the active zone is arranged. The photonic crystal structure can also be arranged between the first and second cladding layers. The cladding layers can form a vertical resonator. In this case, an electric field of the laser mode can be constricted in the vertical direction by a difference in refractive index between the active zone and the cladding layers adjoining it.

In accordance with at least one embodiment or configuration, the laser diode component emits a large part of the laser radiation in a main emission direction, which runs transversely to a main extension plane of the photonic crystal structure. For example, the photonic crystal structure extends in a horizontal plane, while the main emission direction runs in the vertical direction, perpendicular to the horizontal plane.

In accordance with at least one embodiment or configuration, the laser diode component is a PCSEL. A PCSEL is distinguished by at least one of the following features: single-mode operation is also possible with components having larger lateral dimensions of more than 300 µm possible, the laser modes and the beam pattern can be specifically controlled.

In accordance with at least one embodiment or configuration, the crystalline material of the photonic crystal structure is a semiconductor material. The photonic crystal structure can have a crystal layer formed from the crystalline material, which is grown and structured, for example, during the production of the semiconductor layer stack. For example, semiconductor materials based on nitride, such as AlInGaN, or semiconductor materials based on arsenide, such as GaAs, come into consideration as crystalline materials.

In accordance with at least one embodiment or configuration, the structured regions each have a cross section with a polygonal shape, for example with the shape of a regular polygon, parallel to the main extension plane of the photonic crystal structure. In particular, the cross section has a non-round shape. The cross-sectional shape depends, for example, on the crystal system of the crystalline material. In the case of hexagonal crystal systems such as AlInGaN, for example, the structured areas can have triangular or hexagonal cross-sectional shapes. The polygons can have interior angles or central angles of 30° or 60° or multiples or dividers thereof. The angles are therefore dependent on the angles that occur in the crystal system of the crystalline material in question. In the case of cubic crystal systems such as GaAs, for example, the structured areas can have rectangular or octagonal cross-sectional shapes. The polygons can have central angles of 45° or 90° or multiples or dividers thereof.

In accordance with at least one embodiment or configuration, the photonic crystal structure has a cross section with a polygonal shape, for example with the shape of a regular polygon, parallel to its main plane of extension. In particular, the cross section has a non-round shape. As in the case of the structured areas, the cross-sectional shape can depend on the crystal system of the crystalline material. In the case of hexagonal crystal systems such as AlInGaN, for example, the photonic crystal structure can therefore have a triangular or hexagonal cross-sectional shape. The polygons can have internal angles or central angles of 30° or 60° or multiples thereof. The angles are therefore also dependent on the angles that occur in the crystal system of the crystalline material in question. In cubic crystal systems such as GaAs, the photonic crystal structure can have a rectangular or octagonal cross-sectional shape. The polygons can have central angles of 45° or 90° or multiples thereof.

The side face extending on a crystal plane has a comparatively high reflectivity and is therefore suitable as a mirror facet of a photonic crystal structure serving as a resonator. The efficiency of the laser diode component can thus be increased. Furthermore, as a result, the laser diode component can be designed with particularly small lateral dimensions, since no additional mirror elements are required. As a result, the laser diode component can be manufactured particularly cheaply.

In accordance with at least one embodiment or configuration, the boundary surfaces or side surfaces arranged along crystal planes run transversely, preferably perpendicularly, to the main plane of extension of the photonic crystal structure. The boundary surfaces or side surfaces can run, for example, along a or m planes of the crystalline material.

According to at least one embodiment or configuration, the structured areas are depressions in the crystalline material. For example, the structured areas are etched depressions, the final shape and size of which is preferably produced wet-chemically.

A radiation-transmissive medium, for example air or SiO2, which has a refractive index that differs from the refractive index of the crystalline material, can be located in the structured regions.

In accordance with at least one embodiment or configuration, the laser diode component has a reflection layer which is arranged on a side surface of the photonic crystal structure. For example, the reflection layer can be arranged on all side surfaces of the photonic crystal structure. For example, metals with comparatively high reflectivity, such as Au, Al or Ag, or dielectric mirrors come into consideration for the reflection layer. Dielectric and metallic layers can also be combined. The efficiency of the laser diode component can thus be further improved. The reflection layer can comprise a layer sequence made of different materials.

In accordance with at least one embodiment or configuration, the photonic crystal structure has a first lattice structure, which is present in a first region of the photonic crystal structure is assigned and includes a plurality of first structured areas. For example, the first region can be located in a central region of the photonic crystal structure. In the present case, a “lattice structure” is to be understood as meaning a regular arrangement of structured areas, for example.

Furthermore, the photonic crystal structure can have a second lattice structure which is superimposed on the first lattice structure and comprises a plurality of second structured regions, the first structured regions differing from the second structured regions in terms of shape and/or size and/or orientation. Such a configuration of the photonic crystal structure is mode-selective in a special way and enables single-mode operation even in the case of components with smaller lateral dimensions in the range of 10 μm.

Additionally or alternatively, the photonic crystal structure may have a third lattice structure, which is arranged in a second region of the photonic crystal structure adjacent to the first region and comprises a plurality of third structured regions, the first structured regions differing in shape and/or size and/or orientation from the third structured regions. The reflectivity at the side surfaces of the photonic crystal structure can be improved by the third lattice structure. For example, the photonic crystal structure may have a combination of side faces that extend along crystal planes and side faces that laterally delimit a third lattice structure.

In accordance with at least one embodiment or configuration, the laser diode component has a plurality of photonic crystal structures, each of which defines a pixel region. A “pixel area” is to be understood, for example, as a radiation-emitting area of the laser diode component that can be distinguished from a directly adjacent radiation-emitting area. Since the radiation on the side faces of the photonic crystal structures can be reflected back into the pixel areas, it is possible to reduce the crosstalk between the pixel areas and increase the contrast.

For example, the photonic crystal structures of the various pixel regions can be essentially the same, that is to say within the scope of normal manufacturing tolerances. In this way, for example, a display can be produced in which the pixel areas can be controlled individually.

Alternatively, the photonic crystal structures of the different pixel areas can be different. As a result, the radiation characteristics can be varied, for example. For example, emission sources can be generated that emit in different directions depending on the activated pixel areas.

The method described below is suitable for the production of a photonic crystal structure of the type mentioned above. Features described in connection with the photonic crystal structure or the laser diode component can therefore also be used for the method and vice versa.

• - Bereitstellen einer Grundschicht eines kristallinen Materials,
• - Herstellen von strukturierten Bereichen in der Grundschicht, wobei die strukturierten Bereiche jeweils durch zumindest eine Begrenzungsfläche seitlich begrenzt werden,
• - Erzeugen zumindest einer Seitenfläche, welche die zumindest eine photonische Kristallstruktur seitlich begrenzt, wobei zumindest eine Begrenzungsfläche jedes strukturierten Bereichs und/oder zumindest eine Seitenfläche der photonischen Kristallstruktur durch Glätten an Kristallebenen des kristallinen Materials erzeugt wird.

According to at least one embodiment of a method for producing at least one photonic crystal structure for a laser diode component of the type mentioned above, this comprises the following steps:

• - providing a base layer of a crystalline material,
• - Production of structured areas in the base layer, the structured areas each being laterally delimited by at least one boundary surface,
• - Generating at least one side surface which laterally delimits the at least one photonic crystal structure, at least one delimiting surface of each structured region and/or at least one side surface of the photonic crystal structure being produced by smoothing on crystal planes of the crystalline material.

Crystal facets of the crystalline material of the base layer are worked out by the smoothing, resulting in particularly uniform structured areas or highly reflective side surfaces with regard to an alignment of edges and angles, which ensure a high quality of the photonic crystal structure. Furthermore, areas of material damaged by the smoothing can be removed. This results in a lower defect density on surfaces of the structured areas or side faces, which leads to improved efficiency and aging stability in the laser diode component due to lower surface recombination.

In accordance with at least one embodiment or configuration, initial depressions are formed in the base layer to produce the structured regions, and final depressions are produced from the initial depressions by smoothing.

According to at least one embodiment or refinement of the method, the initial depressions are produced by one of the following methods: dry chemical etching, laser ablation. For example, the initial indentations are made smaller than required and smoothed to the final size or shape.

According to at least one embodiment or configuration, an etching process is used for the smoothing. The etching process can be directed to stop on crystal facets of the base layer crystalline material.

For example, the final indentations can be created by wet-chemical smoothing. In the case of GaN as the crystalline material, the wet-chemical smoothing can be carried out with a basic solution as an etchant, for example with KOH or NaOH. In the case of GaAs, on the other hand, acidic solutions such as 3:1:1 H2SO4 (75%):H2O2:H2SO4 (96%), 1:8:80 H2SO4 (96%):H2O2:H2O or 1:8:160 H2SO4 (96%):H2O2:H2O are suitable as etchants.

It is also possible for the final indentations to be produced by dry-chemical smoothing. In this case, the etching process can be conducted in such a way that it is mainly determined by the etchant. In the case of GaN, for example, the etching process can be performed at high temperatures using hydrogen gas as an etchant.

For example, at least one side surface can be generated in a two-stage process analogous to the generation of the structured areas. In this case, in a first process, for example by dry-chemical etching or laser ablation, the base layer can be pre-structured to produce the at least one side surface, and smoothed wet-chemically in a second process after the pre-structuring.

The laser diode components are particularly suitable for display applications, such as head-up displays, for AR (augmented reality) applications, for applications in material processing, for LIDAR (light detection and ranging, also known as light imaging, detection and ranging) systems and for use in hard drives, CD-ROMs and Blu-ray or optical data transmission.

Further advantages, advantageous embodiments and developments result from the exemplary embodiments described below in connection with the figures.

• 1A eine schematische Querschnittsansicht eines Laserdiodenbauelements gemäß einem Ausführungsbeispiel und
• 1B eine schematische Schnittdarstellung einer in dem Laserdiodenbauelement enthaltenen photonischen Kristallstruktur parallel zu einer Haupterstreckungsebene der photonischen Kristallstruktur,
• 2A bis 2D und 3A bis 3F schematische Schnittdarstellungen von Ausschnitten photonischer Kristallstrukturen parallel zu deren Haupterstreckungsebenen gemäß verschiedenen Ausführungsbeispielen,
• 4 eine schematische perspektivische Darstellung eines Laserdiodenbauelements gemäß einem Ausführungsbeispiel,
• 5A und 5B schematische Schnittdarstellungen von photonischen Kristallstrukturen parallel zu deren Haupterstreckungsebenen gemäß verschiedenen Ausführungsbeispielen,
• 6A eine schematische perspektivische Darstellung eines Laserdiodenbauelements gemäß einem Ausführungsbeispiel und
• 6B eine schematische Schnittdarstellung von in dem Laserdiodenbauelement enthaltenen photonischen Kristallstrukturen parallel zu deren Haupterstreckungsebenen,
• 7A und 7B schematische Querschnittsansichten von Verfahrensschritten eines Verfahrens zur Herstellung einer photonischen Kristallstruktur gemäß einem Ausführungsbeispiel.

Show it:

• 1A a schematic cross-sectional view of a laser diode component according to an embodiment and
• 1B a schematic sectional view of a photonic crystal structure contained in the laser diode component parallel to a main extension plane of the photonic crystal structure,
• 2A until 2D and 3A until 3F schematic sectional views of sections of photonic crystal structures parallel to their main extension planes according to various embodiments,
• 4 a schematic perspective view of a laser diode component according to an embodiment,
• 5A and 5B schematic sectional representations of photonic crystal structures parallel to their main extension planes according to various embodiments,
• 6A a schematic perspective view of a laser diode component according to an embodiment and
• 6B a schematic sectional view of photonic crystal structures contained in the laser diode component parallel to their main extension planes,
• 7A and 7B schematic cross-sectional views of method steps of a method for producing a photonic crystal structure according to an embodiment.

In the exemplary embodiments and figures, elements which are the same, of the same type or have the same effect can each be provided with the same reference symbols. The elements shown and their proportions to one another are not necessarily to be regarded as true to scale; Rather, individual elements can be shown in an exaggerated size for better representation and/or for better understanding.

In connection with the 1A and 1B an exemplary embodiment of a laser diode component 1 is described. The laser diode component 1 comprises a semiconductor layer stack 2 which is arranged on a substrate 6 . The substrate 6 can be a growth substrate on which the individual layers of the semiconductor layer stack 2 have grown epitaxially. Alternatively, the substrate 6 can be a carrier replacing the growth substrate. The substrate 6 can be electrically conductive. However, it is also possible for the substrate 6 to be electrically insulating due to its design.

For electrical contacting, the laser diode component 1 has a first contact element 12 on a side of the substrate 6 facing the semiconductor layer stack 2 and on a dem Substrate 6 facing away from the semiconductor layer stack 2, a second contact element 13 on.

The semiconductor layer stack 2 comprises a first semiconductor region 3 of a first conductivity type, for example an n-doped semiconductor region, and a second semiconductor region 5 of a second conductivity type, for example a p-doped semiconductor region, and an active zone 4 arranged between the first and second semiconductor regions 3, 5, which is suitable for emitting laser radiation in the visible spectral range. The first and second semiconductor regions 3, 5 can each have a sequence of individual layers, some of which can be undoped or slightly doped.

The materials already mentioned above are suitable for the semiconductor regions 3 , 4 , 5 or individual layers of the semiconductor layer stack 2 . As an example, in the case of the 1A and 1B illustrated embodiment based on an arsenide compound semiconductor based material. The active zone 4 can emit laser radiation from the red to infrared spectral range.

Furthermore, the laser diode component 1 includes a photonic crystal structure 7, which is arranged in the semiconductor layer stack 2 in this exemplary embodiment. The photonic crystal structure 7 is arranged close to the active zone 4 and is located between a first cladding layer 10 arranged in the first semiconductor region 3 and a second cladding layer 11 arranged in the second semiconductor region 5, between which the active zone 4 is also arranged. The photonic crystal structure 7 is provided in the laser diode component 1 in particular as a lateral resonator, while the cladding layers 10, 11 preferably form a vertical resonator. The laser diode component 1 is preferably a PCSEL.

The photonic crystal structure 7 contains a crystalline material 8 and has a plurality of structured regions 9 . The structured regions 9 are, in particular, depressions in the crystalline material 8. The crystalline material 8 can be epitaxially deposited as a crystalline layer, for example during the production of the semiconductor layer stack 2, and structured accordingly, preferably etched, to produce the structured regions 9. The same materials as for the individual layers of the semiconductor regions 3, 4, 5 of the semiconductor layer stack 2, ie for example semiconductor materials based on arsenide, can be used for the crystalline material 8. A radiation-transmissive medium, for example air or SiO 2 , which has a refractive index that differs from the refractive index of the crystalline material 8 , can be located in the structured regions 9 .

The structured regions 9 are each delimited laterally by at least one boundary surface 7A, which extends along a crystal plane of the crystalline material 8 . The structured regions 9 are preferably delimited on all sides by boundary surfaces 7A which run along crystal planes of the crystalline material 8 . In particular, the boundary surface 7A extending along a crystal plane is in each case a crystal facet of the crystalline material 8.

How out 1B shows that the structured regions 9 each have a cross section parallel to a main extension plane E of the photonic crystal structure 7 which has a rectangular or square shape. Furthermore, the photonic crystal structure 7 parallel to the main extension plane E has a rectangular cross section.

The cross-sectional shape of the structured areas 9 depends on the crystal system of the crystalline material. In cubic crystal systems such as GaAs, the structured areas 9 can be rectangular (cf. also 2A and 2 B) or octagonal cross-sectional shapes (cf. 2C and 2D ) exhibit. The polygons have central angles of 45° or 90°. For example, the boundary surfaces 7A arranged along crystal planes run perpendicular to the main extension plane E of the photonic crystal structure 7.

An alignment of the structured areas 9 on crystal planes leads to particularly smooth and uniform structures and thus to a high quality of the photonic crystal structure 7. The efficiency and service life of the laser diode component 1 can thereby be increased.

The structured regions 9 can have dimensions a1 parallel to a first lateral direction L1 and dimensions a2 parallel to a second lateral direction L2, each in the range of a wavelength of the laser radiation and thus in the range of fractions of a micrometer. In addition, distances d between the structured areas 9 parallel to the first and second lateral direction L1, L2 can be in the range of a wavelength of the laser radiation and thus in the range of fractions of a micrometer.

The structured areas 9 are arranged regularly in the photonic crystal structure 7 and cause a periodic change in the refractive index. How out 1B shows that the structured areas 9 can form a two-dimensional point lattice in a cubic crystal system, such as in GaAs.

The laser diode component 1 has a reflection layer 14 which is arranged on side faces 7B of the photonic crystal structure 7 . For example, metals with comparatively high reflectivity such as Au, Al or Ag or dielectric mirrors come into consideration for the reflection layer 14 . Dielectric and metallic layers can also be combined. The efficiency of the laser diode component 1 can thus be further improved.

The laser diode component 1 emits a large part of the laser radiation in a main emission direction H, which runs parallel to a vertical direction V and transverse to the main extension plane E of the photonic crystal structure 7 .

Based on 2A until 2D further exemplary embodiments of photonic crystal structures 7 are described which have a crystalline material with a cubic crystal system such as, for example, GaAs. The structured areas 9, 9A, 9B have polygonal cross-sectional shapes with central angles α of 45° or 90° or dividers or multiples thereof.

How out 2A shows, the photonic crystal structure 7 can comprise a first lattice structure with a plurality of first structured regions 9A, which each have a rectangular or square cross-sectional shape. Furthermore, the photonic crystal structure 7 can have a second lattice structure which is superimposed on the first lattice structure and comprises a plurality of second structured regions 9B, the second structured regions 9B also each having a rectangular or square cross-sectional shape. However, the second structured areas 9B are larger than the first areas 9A, so that the boundary surfaces 7A have correspondingly longer edges a1, a2.

The first lattice structure can have a pattern of polygons, for example hexagons, with a first structured area 9A being arranged at each corner of a polygon and further first structured areas 9A being arranged in some cases between the corners. Furthermore, the second lattice structure can be a two-dimensional point lattice, with a second structured area 9B being arranged at each lattice point. In this case, a second structured region 9B is arranged within a polygon of the first lattice structure. Such a configuration of the photonic crystal structure 7 is mode-selective in a special way and enables single-mode operation of the laser diode component 1 even with smaller lateral dimensions in the range of 10 μm.

At the in 2 B illustrated embodiment, the structured areas 9 have the same shape, size and orientation. They are rectangular, but not square, and are delimited by delimiting surfaces 7A of different edge lengths a1, a2. As a result, the refractive index changes in the two lateral directions L1, L2 with different periods, which can have a mode-selective effect. The structured areas 9 are arranged at lattice points of a two-dimensional point lattice.

Furthermore, the structured areas 9 as in the 2C and 2D shown each have an octagonal cross-sectional shape. While the boundary surfaces 7A in the in 2C illustrated embodiment each have the same edge lengths, they are in the in 2D illustrated embodiment different, which as in the 2 B illustrated embodiment can act mode-selectively. In these exemplary embodiments too, the structured areas 9 each have the same shape, size and orientation.

Based on 3A until 3F further exemplary embodiments of photonic crystal structures 7 are described which have a crystalline material with a hexagonal crystal system such as, for example, AlInGaN. The structured areas 9, 9A, 9B have in particular polygonal cross-sectional shapes with internal angles α or central angles α of 30° or 60° or dividers or multiples thereof. The boundary surfaces 7A or crystal facets that form correspond, for example, to the a or m plane of the crystal structure.

For example, the structured areas 9, 9A, 9B as in FIGS 3A until 3C shown have a triangular cross-sectional shape. According to the 3A illustrated embodiment, the structured areas 9 are arranged at lattice points of a two-dimensional point lattice and have the same shape, size and orientation. In contrast, the first structured areas 9A in the embodiment of FIG 3B have a different orientation than the second structured regions 9B and are rotated by 180° with respect to them. The photonic crystal structure 7 has a first lattice structure with a pattern of triangles and a second lattice structure superimposed on the first lattice structure with a pattern of triangles, the structured Regions 9A, 9B are located at corners of the triangles, respectively. In this case, a first region 9A is located within a triangle of the second lattice structure and vice versa. At the in 3C illustrated embodiment, the photonic crystal structure 7 is a combination of two lattice structures analogous to those in FIGS 3A and 3B Lattice structures shown, wherein individual lattice areas of a lattice structure are replaced by lattice areas of the other lattice structure.

Furthermore, the structured areas 9, 9A, 9B as in FIGS 3D and 3E shown have a hexagonal cross-sectional shape. While the boundary surfaces 7A in the in 3D illustrated embodiment each have the same edge lengths, they are in the in 3E illustrated embodiment different, which as in the 2 B respectively 2D illustrated embodiments can act mode-selectively. Also in the embodiments of 3D and 3E the structured areas 9 each have the same shape, size and orientation.

Furthermore, the structured areas 9A, 9B, as in the case of 3F illustrated embodiment differ in their form. In this case, the first structured regions 9A have a triangular cross-sectional shape, while the second structured regions 9B are hexagonal. The grid arrangement corresponds to that in connection with 3B lattice arrangement explained and has a superposition of two lattice structures, each having a pattern of triangles, with a first region 9A being located inside a triangle of the second lattice structure and vice versa.

Based on 4 a further exemplary embodiment of a photonic crystal structure 7 in a laser diode component 1 is described. The photonic crystal structure 7 is laterally delimited by side surfaces 7B, that is to say in particular in directions parallel to the main plane of extension, which each extend along a crystal plane of the crystalline material 8 . In particular, the side surfaces 7B are crystal facets of the crystalline material 8, which can be made particularly smooth using the method described here. The side surfaces 7B thus have a comparatively high reflectivity and are particularly suitable as mirror facets of a high-quality photonic crystal structure 7 serving as a resonator. As a result, the efficiency of the laser diode component 1 can be increased. Furthermore, as a result, the laser diode component 1 can be designed with particularly small lateral dimensions, since additional mirror elements can be dispensed with.

The photonic crystal structure 7 has a polygonal cross-sectional shape, which can depend on the crystal system of the crystalline material 8 . For example, the photonic crystal structure 7 can have an octagonal cross-sectional shape in a cubic crystal system such as GaAs.

The side surfaces 7B form a border of the photonic crystal structure 7. In particular, the structured regions 9 are arranged at a distance from the border, which leads to an in-phase reflection.

The boundary surfaces 7A of the structured regions 9 can extend along crystal planes of the crystalline material 8, as described in connection with the previous exemplary embodiments. However, it is also possible for the boundary surfaces 7A to deviate from the crystal planes and for example to have a round shape. The efficiency of the laser diode component 1 can already be increased by the higher reflectivity of the side surfaces 7B aligned with crystal planes.

Based on 5A and 5B further exemplary embodiments of a photonic crystal structure 7 are described. In these exemplary embodiments, the photonic crystal structures 7 are each partially delimited by side faces 7B, which extend along a crystal plane of the crystalline material 8, and partially by side faces 7C, which deviate from crystal planes of the crystalline material 8. A combination of different side faces 7B, 7C is advantageous, for example, if the cross-sectional shape of the photonic crystal structure 7 is to assume a shape that deviates from the crystal system. If, for example, a rectangular shape is to be realized on a hexagonal crystal lattice such as GaN, as in FIGS 5A and 5B shown, two side faces 7B may be formed by crystal facets, while the other two side faces 7C are arranged deviating from crystal planes.

How out 5B shows, the photonic crystal structure 7 can have a first lattice structure comprising a plurality of first structured regions 9A in a first, central region. On the side faces 7C that are not aligned with crystal planes, or in second regions that adjoin the first region, the photonic crystal structure 7 can each have a third lattice structure comprising a plurality of third structured regions 9C, with the first regions 9A, each having a hexagonal cross-sectional shape, differing in shape from the third regions 9C, each having a triangular cross-sectional shape. differentiate. The reflectivity on the side surfaces 7C that are not aligned with crystal planes can be improved by the third lattice structures.

Based on 6A and 6B a further exemplary embodiment of a laser diode component 1 is described. The laser diode component 1 has a plurality of photonic crystal structures 7 which each define a pixel area or a radiation-emitting area of the laser diode component 1 . The photonic crystal structures 7 can be arranged on a common semiconductor layer stack 2 . Alternatively, it is possible for the laser diode component 1 to have a plurality of semiconductor layer stacks, on each of which a photonic crystal structure is arranged.

The photonic crystal structures 7 can be embodied as described in connection with the further exemplary embodiments. For example, the photonic crystal structures 7 of the different pixel areas can essentially be the same, that is to say within the scope of usual manufacturing tolerances. In this way, for example, a display can be produced in which the pixel areas can be controlled individually. Alternatively, the photonic crystal structures 7 of the different pixel areas can be different. As a result, the radiation characteristics can be varied, for example. For example, emission sources can be generated that emit in different directions depending on the activated pixel areas. Since the radiation on the side faces 7B of the photonic crystal structures 7 can be reflected back into the pixel areas, it is possible to reduce the crosstalk between the pixel areas and to increase the contrast. Furthermore, the photonic crystal structures 7 make it possible for the pixel regions to be formed with a smaller size and to be arranged with smaller distances.

In connection with the 7A and 7B an exemplary embodiment of a method for producing at least one photonic crystal structure 7 for a laser diode component of the type mentioned above is described.

The method comprises a step of providing a base layer 15 of a crystalline material 8 (cf. 7A) . For example, the base layer 15 can be applied to a semiconductor layer sequence 18 which is provided for producing the semiconductor layer stack of the laser diode component.

The method also includes a step of producing structured areas 9, the structured areas being laterally delimited in each case by boundary surfaces 7A. The method also includes a step of producing side surfaces 7B, which laterally delimit the at least one photonic crystal structure 7 (cf. 7B) .

In order to produce the structured regions 9, initial depressions 16 are formed in the base layer 15 and final depressions 17 or structured regions 9 are produced from the initial depressions 16 by smoothing. At this time, the smoothing is performed on crystal planes of the crystalline material 8 of the base layer 15 .

Crystal facets of the crystalline material 8 of the base layer 15, which form the boundary surfaces 7A, are worked out by the smoothing. With regard to an alignment of edges and angles, this can result in particularly uniform final depressions 17 or structured areas 9 .

For example, the initial depressions 16 can be produced by dry chemical etching or laser ablation. Although these methods are more aggressive due to their higher mechanical component than methods with a higher chemical component such as wet-chemical etching, they can still be used in the present case, since damaged material areas, for example, are removed by the subsequent smoothing. The removal of the damaged material areas results in a lower defect density on the surfaces of the final depressions 17 or the structured areas 9, which leads to improved efficiency and aging stability in the laser diode component due to lower surface recombination.

The initial depressions 16 are made smaller than required, for example, and brought to the final size or shape by smoothing.

An etching process can be used for smoothing. The final depressions 17 or the structured areas 9 are preferably produced by wet-chemical smoothing. In the case of GaN as the crystalline material, the wet-chemical smoothing can be carried out with a basic solution as an etchant, for example with KOH or NaOH. In the case of GaAs, on the other hand, acidic solutions such as 3:1:1 H2SO4 (75%) :H2O2:H2SO4 (96%), 1:8:80 H2SO4 (96%):H2O2:H2O or 1:8:160 H2SO4 (96%):H2O2:H2O are suitable as etchant.

However, it is also possible that the final wells 17 or the structured Areas 9 are generated by dry chemical smoothing. The etching process can be carried out in such a way that it is mainly determined by the etchant, i.e. the chemical component. In the case of GaN, for example, the etching process can be performed at high temperatures using hydrogen gas as an etchant.

Furthermore, the side surfaces 7B, which delimit the photonic crystal structure 7, can be produced by pre-structuring the base layer 15 and smoothing it along crystal planes of the crystalline material 8 after the pre-structuring. For example, the side surfaces 7B can be produced analogously to the production of the structured areas 9 in a two-stage process. The side surfaces 7B can be defined in a first process, for example by dry chemical etching or laser ablation, and the crystal facets of the crystalline material 8 of the base layer 15, which form the side surfaces 7B, can be worked out in a second process by smoothing, for example by wet chemical etching.

The invention is not limited by the description based on the exemplary embodiments. Rather, the invention encompasses every new feature and every combination of features, which in particular includes every combination of features in the patent claims, even if this feature or this combination itself is not explicitly specified in the patent claims or exemplary embodiments.

Reference List

1

laser diode device

1A

top

2

semiconductor layer stack

3

first semiconductor area

4

active zone

5

second semiconductor area

6

substrate

7

photonic crystal structure

7A

boundary surface

7B, 7C

side face

8th

crystalline material

9

structured area

9A

first structured area

9B

second structured area

9C

third structured area

10

first coat layer

11

second coat layer

12

first contact element

13

second contact element

14

reflective layer

15

base layer

16

initial deepening

17

final deepening

18

semiconductor layer sequence

a

angle

a1, a2

dimension, edge length

i.e

Distance

E

main extension level

H

main emission direction

L1

first lateral direction

L2

second lateral direction

V

vertical direction

Claims (17)

Laser diode component (1) comprising - a semiconductor layer stack (2) which has an active zone (4) for emitting laser radiation, - comprising a photonic crystal structure (7). - a crystalline material (8), - a plurality of structured areas (9, 9A, 9B, 9C), each of which is laterally delimited by at least one delimiting surface (7A), and - at least one side surface (7B, 7C) which laterally delimits the photonic crystal structure (7), at least one of the delimiting surfaces (7A) of the structured regions (9, 9A, 9B, 9C) and/or at least one of the side surfaces (7B, 7C) of the photonic crystal structure (7) extending along crystal planes of the crystalline material (8). Laser diode component (1) according to the preceding claim, wherein the structured regions (9, 9A, 9B, 9C) each have a cross section with a polygonal shape parallel to a main extension plane (E) of the photonic crystal structure (7). Laser diode component (1) according to the preceding claim, which emits a large part of the laser radiation in a main emission direction (H) which runs transversely to the main extension plane (E). Laser diode component (1) according to one of the preceding claims, wherein the structured regions (9, 9A, 9B, 9C) are depressions in the crystalline material (8). Laser diode component (1) according to one of the preceding claims, wherein the crystalline material (8) of the photonic crystal structure (7) is a semiconductor material. Laser diode component (1) according to one of the preceding claims, wherein the photonic crystal structure (7) is arranged in the semiconductor layer stack (2). Laser diode device (1) according to one of the preceding claims, wherein the photonic crystal structure (7) has a first lattice structure which is arranged in a first region of the photonic crystal structure (7) and comprises a plurality of first structured regions (9A). Laser diode component (1) according to the preceding claim, wherein the photonic crystal structure (7) has a second lattice structure which is superimposed on the first lattice structure and comprises a plurality of second structured regions (9B), the first structured regions (9A) differing in shape and/or size and/or orientation from the second structured regions (9B). Laser diode component (1) according to one of the two preceding claims, wherein the photonic crystal structure (7) has a third lattice structure which is arranged in a second region of the photonic crystal structure (7) adjoining the first region and comprises a plurality of third structured regions (9C), the first structured regions (9A) differing in shape and/or size and/or orientation from the third structured regions (9C). Laser diode component (1) according to one of the preceding claims, in which the photonic crystal structure (7) has a cross section with a polygonal shape parallel to its main extension plane (E). A laser diode device (1) as claimed in any preceding claim, comprising a plurality of photonic crystal structures (7) each defining a pixel region. Method for producing at least one photonic crystal structure (7) for a laser diode component (1) according to one of the preceding claims, comprising: - providing a base layer (15) of a crystalline material (8), - Production of structured areas (9, 9A, 9B, 9C) in the base layer (15), the structured areas (9, 9A, 9B, 9C) each being laterally delimited by at least one boundary surface (7A), - Creating at least one side surface (7B, 7C) which laterally delimits the at least one photonic crystal structure (7), at least one delimiting surface (7A) of each structured region (9, 9A, 9B, 9C) and/or at least one side surface (7B, 7C) of the photonic crystal structure (7) being produced by smoothing on crystal planes of the crystalline material (8). Method according to the preceding claim, wherein initial depressions (16) are formed in the base layer (15) to produce the structured regions (9, 9A, 9B, 9C) and final depressions (17) are produced from the initial depressions (16) by smoothing. Method according to the preceding claim, wherein the initial depressions (16) are produced by one of the following methods: dry chemical etching, laser ablation. Method according to one of the two preceding claims, wherein the final indentations (17) are produced by wet-chemical smoothing. Method according to one of Claims 12 until 15 , wherein the base layer (15) for producing at least one side surface (7B, 7C) is prestructured by one of the following methods: dry chemical etching, laser ablation. Method according to the preceding claim, wherein the base layer (15) for producing the at least one side surface (7B, 7C) is wet-chemically smoothed after the pre-structuring.

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